Insulating material

ABSTRACT

An asbestos sheet material, particularly suitable for use as thermal insulation in an emission control device for internal combustion engines, consisting of chrysotile asbestos fibers and elastomeric binder comprising a high molecular weight copolymer of butadiene, the major portion of the asbestos fibers in the sheet being oriented in substantially parallel relation with respect to each other. Prior to use, the sheet is heat treated at a temperature of 525* to 575*F. for a period of time to cause a weight reduction of 8-10 percent.

United States Patent 1191 DOlier June 28, 1974 [54] INSULATING MATERIAL3,509,017 Z1970 Accountius 161/2/06 3,597,514 1971 J 26443 [75] Invento"Gem'ge Doll", Devon Com 3,694,304 9/1972 PififililbO 161/68 [73]Assigneez RaybestwManhattan Inc 3,703,396 11/1972 Lamanche et a1. 117/21Stratford, Conn. Primary Examiner-George F. Lesmes [22] Filed: Apr. 28,1972 [52] U.S. Cl. 161/60, 23/288 F, 156/306,

161/70, 161/170, 161/205, 260/415 R [51] Int. Cl B32b 5/12, B32b 13/12,B01j 9/00 [58] Field of Search 161/60, 70, 170, 205

[56] References Cited UNITED STATES PATENTS 2,534,814 12/1950 DOlier260/415 2,626,213 l/l953 Novak 92/3 2,668,142 2/1954 Strecker 196/503,449,202 6/1969 Bowen l6l/l70 Assistant Examiner-William R. Dixon, Jr.

[ 7] ABSTRACT An asbestos sheet material, particularly suitable for useas thermal insulation in an emission control device for internalcombustion engines, consisting of chrysotile asbestos fibers andelastomeric binder comprising a high molecular weight copolymer ofbutadiene, the major portion of the asbestos fibers in the sheet beingoriented in substantially parallel relation with respect to each other.Prior to use, the sheet is heat treated at a temperature of 525 to 575F.for a period of time to cause a weight reduction of 8-10 percent.

6 Claims, 4 Drawing Figures PATENTED was 1924 FIGI.

ENGINE FIG.4.

Flea. I

L l I l l l 1 INSULATING MATERIAL BACKGROUND OF THE INVENTION One of themain sources of atmospheric pollution is exhaust emissions from internalcombustion engines. In view thereof both federal and state governmentshave enacted legislation establishing emission standards with the viewto improving mans environment. In order to meet such standards, theautomotive industry is en gaged in extensive research for ways to reducethe amount of pollutants, such as unburned hydrocarbons, carbonmonoxide, and nitrogen and sulfur oxides, in the exhaust emissions frominternal combustion engines. Proposals to reduce pollution includeimproved combustion of fuel, recycle of a portion of exhaust gases, andtreatment of exhaust gases to convert pollutants into non-pollutingforms, e.g. carbon dioxide and water vapor.

With respect to the treatment of exhaust emissions from internalcombustion engines, it has been proposed to pass the exhaust gasesthrough a thermal reactor designed to maintain the gases at a relativelyhigh temperature on the order of l,6002,000F. An oxidizing gas, such asair, is also introduced to the reactor, whereby unburned hydrocarbonsand carbon monoxide are converted into such non-polluting substances ascarbon dioxide and water vapor. The reactor can also contain a catalystsuch as platinum, which promotes such reactions.

Because certain equipment, e.g., rubber hose, plastic fittings, etc.,located in the engine compartment of a motor vehicle is incapable ofwithstanding very high temperatures, the compartment temperature mustnot be permitted to exceed a given maximum, otherwise such equipmentwould be degraded and ultimately destroyed. Thus, the exhaust manifoldand other engine parts are so designed that the exterior surfacesthereof do not exceed about900F.

As noted above, in order to obtain the necessary conversion ofpollutants to non-polluting forms, reaction temperatures of l,600F. orgreater are required. Thus, thermally insulating the reactor from theengine compartment is required. For such purpose it has been proposed touse a thermal insulating material consisting of a sheet of asbestosfibers bonded together by an inorganic binder, such as sodium silicate.Unfortunately, because of the vibratory forces which are present duringoperation of a motor vehicle, such insulation, which is relativelybrittle, rapidly disintegrates and loses its insulating properties.

U.S. Pat. No. 2,534,814 discloses a compressed sheet material consistingof asbestos fibers and vulcanized rubber (natural or syntehtic).Although such sheet has some degree of resiliency, as well as thermalinsulating properties; nevertheless, upon being heated rapidly totemperatures above 500F., the sheet badly blisters and loses bothinsulating properties and strength in the blistered areas. It is,therefore, unsatisfactory as an insulating material for thermal reactorsfor internal combustion engines.

OBJECTS OF THE INVENTION It is a primary object of the present inventionto provide a novel thermal insulating material comprising chrysotileasbestos fibers and elastomeric binder.

Another object of this invention is to provide a thermal insulatingmaterial which is resilient and which retains its thermal insulatingpropezrtiesand a significant degree of resiliency when heated totemperatures on the order of 700 to 1,200F.

Still another object of the present invention is a method for producingan improved thermal insulating material comprising chrysotile asbestosfibers and elastomeric binder, which method involves a novel heattreatment.

Yet another object of this invention is an improved thermal reactor fortreating exhaust emissions from internal combustion engines to reducethe quantity of pollutants introduced to the atmosphere.

These and other objects of this invention will be read ily understood byreference to the specification, appended claims and drawings, in which:

FIG. 1 is a plan view showing schematically an internal combustionengine. having attached thereto an emission control device according tothis invention, with parts broken away;

FIG. 2 is a fragmentary end elevation of FIG. 1 as viewed from the left;

FIG. 3 is a transverse section of an emission control device of thisinvention taken along the line 3--3 of FIG. 1, and

FIG. 4 is a greatly enlarged sectional view showing the details of thatportion of the insulating means of the emission control device containedwithin the circle marked FIG. 4" in FIGS.

According to this invention, there is provided a novel method of makinga heat insulating material which comprises forming a sheet comprisingchrysotile asbestos fibers and an elastomeric binder comprising a highmolecular weight copolymer of butadiene, the major portion of theasbestos fibers being oriented in a generally parallel relation withrespect to each other within said sheet, and heat treating said sheet ata temperature of from about 525 to about 5 F. for a period of time tocause a weight reduction in said sheet of from about 8 to about 10percent.

Preferably, the sheet, prior to the stated heat treatment, is producedaccording to the method of US. Pat. No. 2,534,814, discussed in greaterdetail hereinafter.

This invention also contemplates a novel emission control devicecomprising a reaction chamber, means surrounding and supporting thereaction chamber, and heat insulating means comprising a plurality ofsuperimposed layers of the novel asbestos sheet material of thisinvention being located between the reaction chamber and supportingmeans.

It was discovered that by fonning a sheet of chrysotile asbestos. fibershaving as a binder certain high molecular weight copolymers ofbutadiene, particularly certain butadiene-styrene copolymers, andsubjecting such sheet to a particular heat treatment, there is obtainedan insulating material having a significant degree of resiliency atrelatively high temperatures on the order of 700 to 1,200F. At thesetemperatures the sheet does not undergo degradation to any significantdegree. Thus, the sheet is capable of being subjected to substantialvibratory forces without breaking down even at the above-statedsubstantially elevated temperatures.

By reason of such properties, it was found that the novelasbestos sheetwas an effective heat insulating means in emission control devices formotor vehicle internal combustion engines. More specifically, when twoor more layers of the thermal insulating material are used as the heatinsulating means of an emission control device, commonly referred to inthe automotive industry as a thermal reactor (described in detailhereinafter in connection with the drawings), although the inner layerwhich is in direct contact with the reaction chamber is degraded byreason of the very high temperatures, e.g., l,600-2,000F., to which itis exposed, the outer layer or layers which are at somewhat lowertemperatures, e.g., 700l ,200F., are not significantly degraded andretain their resiliency and structural integrity. Thus, the insulatingmaterial of this invention has solved the problem of insulating varioustypes of emission control devices for internal combustion engines.

DETAILED DESCRIPTION OF THE liNVENTlON Theheat insulating material ofthis invention is composed of two essential materials namely, chrysotileasbestos fibers and certain types of elastomeric binder.

The chrysotile asbestos fibers preferably are relatively long fibers,such as those having the Standard Grade Designation SR and longer,including crude fibers, as classified by the Quebec Standard AsbestosTesting Machine. Fibers having the Standard Grade Designation SR orlonger are particularly preferred where the initial sheet, prior to theheat treatment, is prepared on a compressed asbestos sheeter accordingto the method of US. Pat. No. 2,534,814. However, shorter fibers than 5Rmay be used where the initial sheet is formed on a fourdrinier machineaccording to the method of US. Pat. No. 2,636,213, describedhereinafter. However, the initial sheet, before heat treatment,preferably is formed on a compressed asbestos sheeter.

Turning now to the binder, it should comprise an elastomeric material.The term elastomeric as used in this specification and appended claims,is to be given its art recognized meaning and refers to materials thatpossess mechanical properties similar to the special propertiescharacteristic of natural rubber high deformability, rapid recovery fromdeformation, good mechanical strength, etc. The elastomeric materialspreferably employed as binders are high molecular weight copolymers ofbutadiene, such as butadienestyrene and butadieneacrylonitrilecopolymers, particularly the former. By high molecular weight is meantthose butadiene copolymers having a molecular weight in the rangebetween about 150,000 and 200,000. in the case of butadiene-styrene(SBR) copolymers, preferably they contain from about 20 to about 30percent,

by weight, of bound styrene. Particularly useful SBR copolymers containon the order of 28-29 percent bound styrene.

As will be seen from the following discussion, the elastomeric binderordinarily will be combined with the asbestos fibers in the form of alatex, regardless of whether the initial sheet is formed on a compressedasbestos sheeter or on a fourdrinier machine. Suitable latices generallywill contain a relatively high solids content, e.g., 65-70 percent totalsolids. Such latices have an alkaline pH and contain a soap-typeemulsifier or dispersing agent.

The relative proportions of asbestos and elastomeric binder may varysomewhat as shown by the following table; -Continued Constituent Percentby Weight sirable holes.

Constituent Percent by Weight Preferably, the sheet comprises aboutpercent asbestos fibers, 15, percent elastomeric binder and 10 percentfiller,

Suitable fillers include barium sulfate, calcium carbonate, zinc oxide,magnesium oxide and the like. The filler particles preferably are 200mesh. The sheet may also contain the usual curing agents, curing agentaccelerators, etc. Preferably, the sheet does not contain any curingagent.

As stated above, the asbestos fibers and elastomeric binder may becombined to form a sheet by means of the method of US. Pat. No.2,534,814. According to that patent, the asbestos fibers are firstcoated with a rubber solvent, such-as gasoline, mineral spirits,petroleum naphtha, etc'., in suitable mixing apparatus, such as akneader. Thereafter, the latex and filler, curing agents, etc., if any,are added to the kneader. The resulting mix, which should be of sheeterconsistency, is fed to the nip of the rolls of a compressed asbestossheeter. Such apparatus, which is generally similar to a rubber mill,has rolls of two different diameters which run at even speeds. Thelarger roll, which is the bulidup roll, is heated to a temperature of240 270F. and the smaller roll is run cold. A tremendous pressure isapplied by the cold roll which is continuously backed off during thebuild up operation to the desired sheet thickness. As the materialbuilds up, solvent is evaporated.

On the sheeter the major portion of the asbestos fibers become alignedin a generally parallel relation extending circumferentially of theroll. in most instances on the order of 60-70 percent of the fibers willbe so aligned. Such alignment of the fibers is important in providingthe sheet with desirable physicalproperties.

The sheet produced on the sheeter will generally have a thickness in therange between about 1/64 in. and l/l6 in. "depending upon the particularuse for which the sheet is designed. The sheet from the sheeter shouldhave. a density of about 1.00 oz./cu.in. (10.03 oz. If the desnity istoo low, the sheet may have unde- In an altemativeembodiment of thisinvention, the initial asbestos sheet can be produced on a fourdriniermachine according to the method of US Pat. No. 2,626,213. In suchprocess a dispersion of asbestos fibers is prepared according to thepatent, rubber latex I is added thereto, and the composition is sheetedon a fourdrinier machine. Such machine also causes the as bestos fibersto be aligned predominantly in a single direction as described above.The proportions of fibers and latex employed should be such as toprovide a sheet containing 65-90 percent fibers and 10-20 percentelastomeric binder.

Regardless of whether the initial sheet is formed on a compressedasbestos sheeter or on a fourdrinier machine, the sheet is subjected tothe identical heat treatment. Broadly, the heat treatment comprisesheating the sheet at a temperature of from about 525F. to about 575F.,preferably about 550F., for a period of time to cause a weight reductionin the sheet of from about 8 to about percent, preferably about 9percent. This heat treatment apparently drives off volatiles such as thelatex soap, residual solvent, etc., and also causes some cracking of theelastomeric binder. In addition, some or all of the hygroscopic(uncombined) water of the asbestos fibers is volatilized.

The removal of such volatiles should be carried out so as to avoid anyshock treatment, otherwise blister formation and degradation of thesheet will occur. Thus, the sheet should be slowly heated to theabovespecified temperature range. A particularly preferred heattreatment comprises heating the sheet from ambient temperature to about400F. over a period of about one hour, maintaining the sheet at about400F. for several hours, e.g. 4 hours, cooling the sheet to ambienttemperature, then heating the sheet to about 550F. over a period of 1hour, followed by maintaining the sheet at the latter temperature forseveral hours, e.g., 2-4 hours.

The above preferred heating schedule can be varied, and to some degreewill depend upon sheet thickness, thicker sheets requiring longerheating times at the specified elevated temperatures.

After the heat treatment, the sheet should have the following physicalproperties:

Tensile Strength across Grain 2800-3200 psi k Factor ,O9-. l4 BTU-Ft/FtHr F Direction of major portion of fiber orientation.

As stated above, the novel asbestos sheet material of this invention isparticularly useful as insulation in emission control devices forinternal combustion engines. Referring to the drawings, 10 representsschematically an internal combustion engine, e.g., a gasoline engine.Attached to the engine by means of four cylinder exhaust ducts 12 isexhaust manifold 14 of cast iron or other suitable metal. Manifold 14 iscomposed of two elongated mating castings l6 and 18 held together by nutand bolt means 20. A gasket 22 to form an airtight seal between castingsl6 and 18 could be used.

Within the elongated recess of the manifold 14 is a generally tubularreaction chamber or can 24 of heat and corrosion resistant material,usually metal such as a nickel-chromium alloy. The reaction chamber isprovided with four flanged exhaust gas intake ports 26 which are seatedin accommodating recessed portions of casting 16 so as to connect withcylinder exhaust ducts 12. The reaction chamber also has a flangedexhaust duct 28 (FIG. 1) which connects with exhaust line 30 attached tomanifold casting 18. The reaction chamber may contain baffles or thelike, not shown.

Completely surrounding the reaction chamber or can 24 is insulationmeans 32 comprising three superimposed layers of the asbestos sheetmaterial of the present invention; Each layer, for example, may be about1/32 in. in thickness. In any event, the total thickness should besufficient to maintain the temperature within the reaction chamber aboveabout l,600F. while preventing the exterior surface of the manifold 14from exceeding about 900F. Preferably, the layers are not bondedtogether.

In operation, exhaust emissions from engine 10, along with an oxidizinggas, such as air, enters the reaction chamber 24 through exhaust ductsl2 and ports 26. In the reaction chamber unburned hydrocarbons andcarbon monoxide are converted to carbon dioxide and water vapor. Thenon-polluting gases are then exhausted through exhaust pipe 30.

During operation, the innermost layer of insulating material (see 32a,FIG. 4) is degraded by contact with the reaction chamber which is at atemperature above l,600F. I-Iowever, insulating layers 32b and 320,particularly the latter which is heated to a temperature generally notexceeding 1,000F., retain both insulating porperties and a sufficientdegree of resiliency to provide the necessary temperature differentialbetween the reaction chamber and the exterior of the manifold eventhough subjected to substantial vibratory forces. Based on tests to datewith exhaust. emission control devices of the general type shown in thedrawings, it is anticipated that the asbestos sheet material of thisinvention will provide effective insulation for a period of engineoperation in excess of 50,000 miles.

The novel asbestos sheet material, in addition to having utility as heatinsulating means in emission control devices (thermal reactors,catalytic converters, etc), can be employed to insulate engine airintake heaters and can be used to form carburetor spacer gaskets oninternal combustion engines. The sheetmaterial thus finds particularutility as heat insulation where such insulation is subjected tovibratory forces.

The following example is illustrative of the invention, and is not to beconsidered as in limitation thereof:

EXAMPLE I Constituent Parts by Weight Butadiene-styrene copolymer latexsolids* Chrysotile asbestos fiber Barrium sulfate 10 Petroleum naphthasolvent I00 'Ilie latex contained 68% solids, and the copolymercontained 28% bound styrene and had a molecular weight in the range ofl50,000 to 200,000.

" Standard Grade Designation 3A and longer (Quebec Standard AsbestosTesting Machine).

The asbestos fibers and solvent were combined in a kneader, the amountof solvent being sufficient to thoroughly coat the fibers. The bariumsulfate and latex were then added to the kneader and mixed with thefibers to provide a kneaded composition of sheeter consistency. The mixwas fed to the nip of the rolls of a compressed asbestos sheeter. Thelarger hot roll of the sheeter was at a temperature of about 260F., atwhich temperature the solvent was driven off. High pressure was appliedby the cold roll which was continuously backed off during the build-upof the sheet on the hot roll. The final sheet had a thickness of about1/32 inch and a density of 1.00 oz./cu.in. (200.03 oz.) when removedfrom the hot roll.

The sheet was cut into several smaller size pieces, and the pieces wereheated from ambient temperature Density: 0.90 oz./cu.in. Durometer C"Scale Hardness: 88 Compression at 5000 psi: 24.0% Compression at I000psi: 19.2%

Tensile Strength with Grain": 8020 psi Tensile Strength across Grain:3052 psi k Factor: .11 BTU-Ft/FF-Hr-"F. Direction of major portion offiber orientation.

Asbestos sheet material produced as in Example I was used as heatinsulation means on an emission control device of the general typedisclosed in the draw ings. The sheet material provided the necessaryheat insulating properties after 50,000 miles of operation of the motorvehicle in which the engine having the emission control device wasinstalled.

The above-described separation of the superimposed layers of the heatinsulating material can be enhanced by coating the surfaces of thematerial with a layer of inorganic material. An effective coating can beobtained by use of the lithium polysilicate solution disclosed in U.S.Pat. No. 2,668,142. In addition, the heat insulating properties of theasbestos sheet material of this invention can be somewhat enhanced byincluding up to about 15 percent of such lithium polysilicate in thesheet per se.

What is claimed is:

l. The method of making a heat insulating material which comprisesforming a sheet comprising from about 75 to about 90 percent by weightof chrysotile asbestos fibers, from about 10 to about 20 percent of anelastomeric binder comprising a copolymer of butadiene having amolecular weight of from about 150,000 to about 200,000, and from aboutto about 10 percent of filler, the major portion of said asbestos fibersbeing oriented in a generally parallel relation with respect to eachother within said sheet, and heat treating said sheet at a temperatureof from about 525 to about 575F. for a period of time to cause a weightreduction in said sheet of from about 8 to about 10 percent and toeffect cracking of said elastomeric binder.

2. The method according to claim 11 wherein said asbestos fibers rangein size from SR to crude, and said elastomeric binder comprises acopolymer of butadiene and styrene.

3. The method according to claim 2 wherein said heat treatment comprisesslowly heating said sheet to about 400F., maintaining said sheet at saidtemperature for a period of several hours, cooling said sheet to ambienttemperature, slowly heating said sheet to about 550F., and maintainingsaid sheet at said latter temperature for a period of several hours.

4. An asbestos sheet comprising from about to about percent by weight ofchrysotile asbestos fibers, from about 10 to about 20 percent of anelastomeric binder comprising a copolymer of butadiene having amolecular weight of from about 150,000 to about 200,000 and from about 0to about 10 percent of filler, the major portion of said asbestos fibersbeing oriented in a generally parallel relation with each other withinsaid sheet, said sheet having been heat treated at a temperature of fromabout 525 to about 575 F., for a period of time to cause a weightreduction in said sheet of from about 8 to about 10 percent and toeffect cracking of said elastomeric binder.

5. An asbestos sheet according to claim 4 wherein said asbestos fibersrange in size from SR to crude, and said elastomeric binder comprises acopolymer of butadiene and styrene.

6. An asbestos sheet according to claim 5 wherein said heat treatmentcomprises slowly heating said sheet to about 400F., maintaining saidsheet at said temperature for a period of several hours, cooling saidsheet to 0 ambient temperature, slowly heating said sheet to about550F., and maintaining said sheet at said latter temperature for aperiod of several hours.

2. The method according to claim 1 wherein said asbestos fibers range insize from 5R to crude, and said elastomeric binder comprises a copolymerof butadiene and styrene.
 3. The method according to claim 2 whereinsaid heat treatment comprises slowly heating said sheet to about 400*F.,maintaining said sheet at said temperature for a period of severalhours, cooling said sheet to ambient temperature, slowly heating saidsheet to about 550*F., and maintaining said sheet at said lattertemperature for a period of several hours.
 4. An asbestos sheetcomprising from about 75 to about 90 percent by weight of chrysotileasbestos fibers, from about 10 to about 20 percent of an elastomericbinder comprising a copolymer of butadiene having a molecular weight offrom about 150,000 to about 200,000 and from about 0 to about 10 percentof filler, the major portion of said asbestos fibers being oriented in agenerally parallel relation with each other within said sheet, saidsheet having been heat treated at a temperature of from about 525* toabout 575* F., for a period of time to cause a weight reduction in saidsheet of from about 8 to about 10 percent and to effect cracking of saidelastomeric binder.
 5. An asbestos sheet according to claim 4 whereinsaid asbestos fibers range in size from 5R to crude, and saidelastomeric binder comprises a copolymer of butadiene and styrene.
 6. Anasbestos sheet according to claim 5 wherein said heat treatmentcomprises slowly heating said sheet to about 400*F., maintaining saidsheet at said temperature for a period of several hours, cooling saidsheet to ambient temperature, slowly heating said sheet to about 550*F.,and maintaining said sheet at said latter temperature for a period ofseveral hours.